Occasionally useful as handsets (though not as much as 2.5mm headset port would be) this 3.5mm port does allow for MP3 Player, Radio and other similar functions to be used with audio transmitted to any standard headphones of the users' choice.

Having the ability to use a 3.5mm headset is also desirable (though that is not standard). Having the 3.5mm stereo headphone capability broken because the phone has headset capability isn't desirable at all though.